Techniklexikon

Actinium

Ac, Element der Nebengruppe III des Periodensystems, der Scandiumgruppe, Ordnungszahl 89. Actinium besitzt die Elektronenkonfiguration [Rn]6d¹7s². Bis jetzt sind 26 radioaktive Isotope bekannt, deren Massenzahlen zwischen 209 und 232 variieren und deren Halbwertszeiten zwischen 8ns und 21,77a liegen. Das Isotop , das ein starker b-Strahler ist, kommt einerseits in der Natur als Zerfallsprodukt von ²³⁵U vor:

 ,

und kann andererseits durch künstliche Elementumwandlung hergestellt werden. Hierzu wird z.B. Radium in einem Reaktor mit Neutronen beschossen:

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Actinium 1: Wichtige Isotope.

bottom-alt:solid black .75pt;padding:0cm 3.55pt 0cm 3.55pt\'> Isotop	bottom:solid black 1.0pt;border-right:none; mso-border-top-alt:solid black .75pt;mso-border-bottom-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'> Natürliche Häufigkeit [%]	bottom:solid black 1.0pt;border-right:none; mso-border-top-alt:solid black .75pt;mso-border-bottom-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'> Atommasse	bottom:solid black 1.0pt;border-right:none; mso-border-top-alt:solid black .75pt;mso-border-bottom-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'> Halbwertszeit T1/2	bottom-alt: solid black .75pt;mso-border-right-alt:solid black .75pt;padding:0cm 3.55pt 0cm 3.55pt\'> Verwendung
225Ac	0	225,023205	10,0 d	Spuren
227Ac	Spuren	227,027750	21,77 a	NMR
bottom:solid black 1.0pt;border-right:none;mso-border-left-alt:solid black .75pt; mso-border-bottom-alt:solid black .75pt;padding:0cm 3.55pt 0cm 3.55pt\'> 228Ac	bottom:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;padding:0cm 3.55pt 0cm 3.55pt\'> Spuren	bottom:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;padding:0cm 3.55pt 0cm 3.55pt\'> 228,031015	bottom:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;padding:0cm 3.55pt 0cm 3.55pt\'> 6,13 h	bottom:solid black 1.0pt;border-right:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;mso-border-right-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'>

 

Actinium 2: Allgemeine, chemische und festkörperphysikalische Eigenschaften.

bottom:none;border-right:none; mso-border-top-alt:solid black .75pt;mso-border-left-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> Ordnungszahl	bottom:none;border-right:solid black 1.0pt; mso-border-top-alt:solid black .75pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'>	bottom:none;border-right:solid black 1.0pt; mso-border-top-alt:solid black .75pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> 89
Dichte (berechnet) [gcm-3]		10,07
bottom:solid black 1.0pt;border-right:none; mso-border-left-alt:solid black .6pt;mso-border-bottom-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'> Molvolumen [cm3]	bottom:solid black 1.0pt;border-right:solid black 1.0pt;mso-border-bottom-alt: solid black .75pt;mso-border-right-alt:solid black .6pt;padding:0cm 3.55pt 0cm 3.55pt\'>	bottom:solid black 1.0pt;border-right:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> 22,54
bottom:solid black 1.0pt;border-right:none; mso-border-left-alt:solid black .6pt;mso-border-bottom-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'> Kristallstruktur	bottom:solid black 1.0pt;border-right:solid black 1.0pt;mso-border-bottom-alt: solid black .75pt;mso-border-right-alt:solid black .6pt;padding:0cm 3.55pt 0cm 3.55pt\'> kdp	bottom:solid black 1.0pt;border-right:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> Gitterkonstante [nm] a = 0,5311
bottom:solid black 1.0pt;border-right:none; mso-border-left-alt:solid black .6pt;mso-border-bottom-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'> Raumgruppe	bottom:solid black 1.0pt;border-right:solid black 1.0pt;mso-border-bottom-alt: solid black .75pt;mso-border-right-alt:solid black .6pt;padding:0cm 3.55pt 0cm 3.55pt\'>	bottom:solid black 1.0pt;border-right:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> Fm3m

 

Actinium 3: Thermische und elektromagnetische Eigenschaften.

bottom:none;border-right:none; mso-border-top-alt:solid black .75pt;mso-border-left-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> Siedetemperatur [K]	bottom:none;border-right:solid black 1.0pt; mso-border-top-alt:solid black .75pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> 3470±300
Schmelztemperatur [K]	1320±50
Siedeenthalpie [kJmol-1]	293
Schmelzenthalpie [kJmol-1]	14,2
Thermischer Längenausdehnungskoeffizient [10-6K-1]	14,9
bottom:solid black 1.0pt;border-right:none; mso-border-left-alt:solid black .6pt;mso-border-bottom-alt:solid black .75pt; padding:0cm 3.55pt 0cm 3.55pt\'> Wärmeleitfähigkeit [Wm-1K-1]	bottom:solid black 1.0pt;border-right:solid black 1.0pt; mso-border-bottom-alt:solid black .75pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> 12,0

 

Actinium 4: Atom- und kernphysikalische Eigenschaften.

bottom:none;border-right:none; mso-border-top-alt:solid black .6pt;mso-border-left-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> Termsymbol	bottom:none;border-right:solid black 1.0pt; mso-border-top-alt:solid black .6pt;mso-border-right-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> 2D3/2
1. Ionisierungsenergie [eV]	5,17
2. Ionisierungsenergie [eV]	12,10
Elektronegativität (Pauling)	1,1
effektive Kernladung (Slater)	1,80
Ionenradius (Ac3+) [nm]	0,118
Atomradius [nm]	0,1878
bottom:solid black 1.0pt;border-right:none; mso-border-left-alt:solid black .6pt;mso-border-bottom-alt:solid black .6pt; padding:0cm 3.55pt 0cm 3.55pt\'> Einfangquerschnitt für thermische Neutronen [barn] (227Ac)	bottom:solid black 1.0pt;border-right:solid black 1.0pt;mso-border-bottom-alt: solid black .6pt;mso-border-right-alt:solid black .6pt;padding:0cm 3.55pt 0cm 3.55pt\'>   810